In the last several decades there has been increasing interest in the study of pyroelectricity and its utility in environmental detection, laser transmission and the like. By pyroelectricity is meant that property of certain crystals to produce a state of electric polarization by a change in temperature, typically as that temperature is changing.
The phenomenon of pyroelectricity is well described in the literature (e.g. Sidney B. Lang, Sourcebook of Pyroelectricity, Gordon and Breach Science Publishers, New York, 1974). The effect appears to result from the enharmonic ionic vibration of crystals lacking a center of symmetry. Typically, the effect is attained by rapidly increasing or decreasing the temperature of an appropriate crystal, substantially above or below ambient, respectively, which in turn will spontaneously generate a voltage along a polar axis of the crystal. Typically, however, when the temperature of such crystal is then maintained at a constant temperature, even at an extreme of increased or decreased temperature, voltage generation ceases and any voltage which may have been built up immediately dissipates, with the crystal becoming externally electrically neutral.
The utility of pyroelectric crystals in the prior art has generally closely followed the typical aforedescribed experience with the phenomenon. Heat detection, light detection and/or radiation detection, wherein a crystal will be caused to undergo a temperature change by exposure to heat, light and/or radiation, have become the major utilities of pyroelectrics. The voltage generated by a temperature change is measured to quantify heat, light or radiation change. Such utilities are commercially important, but the inability of present pyroelectric crystals to store the voltage generated, together with the typical necessity of, for example, altering the temperature above or below ambient, to achieve an effect in such crystals, has been a severe limitation to their practical application.